奥数数学题1+1/3+1/6+1/10+1/15+1/21+1/28+1/36+1/45+1/55简便运算急~

分母：1,3,6,10……n(n+1)/2∴原式=2/(1*2)+2/(2*3)+2/(3*4)+……+2/(10*11)=2[(1-1/2)+(1/2-1/3)+……+1/10-1/11]=2(1-1/11)=20/11=1又9/11后面一题跟前面差不多,原式=1+1/3+1/6+1/10+……+1/(1+……+n)=2{1/(1*2)+1/(2*3)+……+1/[n(n+1)]}=2[1-1/2+1/2-1/3+……+1/n-1/(n+1)]=2[1-1/(n+1)]=2n/(n+1)